How come the letters representing the different
blood types go in the order "A", "B", and then
"O"... why not "A", "B", and then "C", wouldn't
it make more sense to go along with the
alphabetical order?

Question Date: 2003-01-08

Answer 1:

This is a very good question, because you're
right, at first the ABO convention for
blood typing seems a little illogical.
However, the story of why we use an O
instead of a C actually turns out to be an
interesting one, and in the end it makes sense.

The importance of blood was recognized back in
ancient times, but the way in which it actually
worked and moved about the body remained a
mystery. It wasn't until 1616 that the
circulation of blood was properly described by
the Englishman William Harvey. His discovery
was a major advance in medicine and physiology,
and represented a radical departure from over a
thousand years of thought on the movement of blood
in the body (in fact, because his theory
challenged so many centuries of medical belief, he
hesitated until 1628 to publish his ideas). His
discovery also made possible a new form of
treatment: blood transfusion.

By the mid-1600s several physicians were
experimenting with blood transfusion with mixed
success; within ten years, in response to some of
the more spectacular failures, France, Italy, and
Britain had each enacted regulations prohibiting
the transfer of blood from animals to humans. (At
that time physicians were unaware of differences
in blood between animals and humans, and also did
not yet know about germs and the diseases that
could be introduced through animal-human
transfusions. It's easy to see how some of these
experiments could turn out very badly!) By the
late 1800s transfusions were considered a highly
promising yet risky procedure. While the
successes were encouraging, in far too many cases
the red blood cells would clump together
(agglutinate) in the patient upon transfusion,
often resulting in death. The doctors of the time
thought this clumping was due to some sort of
disease in the patient.

Karl Landsteiner, a pathologist in
Vienna, wasn't convinced. He decided to
perform some experiments in which he collected
blood from many volunteers and then crossed the
red blood cells and blood serum between donors in
various combinations. He recorded which
combinations resulted in agglutination and
which did not, and during the course of his
experiments he began to notice a pattern. In
papers published in 1900 and 1901 he related his
findings, asserting that there were three
different groups or types of blood found in
people. He claimed that the agglutination
people had so often observed after transfusion was
not due to illness or disease, but rather was the
result of crossing incompatible types. You may be
surprised to learn the names he assigned to the
three blood groups he identified. He called them
types A, B, and C-- just as you suggested!

A year later, two of Landsteiner's students,
Alfred von Decastello and Adriano Sturli,
discovered the fourth (and most rare) blood type,
AB. Landsteiner and his colleagues later
decided to change the name of blood type C to
O in order to indicate that it is unique from
the other blood types in that it lacks surface
antigens.

I'm not sure why they chose the letter
O, but for me it has always seemed
intuitive, and it makes it easy to remember how
this blood type is different. Type A red blood
cells have A antigens on their surfaces, and type
B red blood cells have B antigens on their
surfaces. Type AB blood have both the A and B
antigens on their surfaces. If type O
blood
still was designated with a C, we might be
inclined to think that it possesses C antigens.
By naming it with an O instead, we are
reminded automatically that it is different, and I
have always imagined a round cell with smooth
surface-- just like the letter O!-- and
zerO
antigens. I don't know if that's what
Landsteiner and his colleagues were also thinking
when they chose the letter O, but I'd like to
think so!

Landsteiner's discovery was incredibly
important, because it finally made blood
transfusion a viable, safe option for treatment.
This procedure has since saved countless lives.
It was also recognized that blood type was
heredity, allowing police and others to test
blood to determine if people could be related or
to see if a suspect matched the blood found at a
crime scene. Because his discovery was so
important, Karl Landsteiner received the Nobel
Prize in Medicine in 1930.